I have pasted a bash script that cross-compiles libtiff
version 3.9.6 on a Mac for iOS 6.1 to be used on devices and in the simulator. You will have to adapt it to your needs. Also see this tutorial for hints. It creates a fat library for both compilation targets.
rakmohs answer is also correct, but only part of the solution. You add the folder with the fat library in the "Add Other.." dialogue he proposes.
Then you also add libz.dylib! After that, I could use libtiff
in my app on my device and on the simulator.